This invention relates to methods and apparatuses for packaging microelectronic devices; more particularly, this invention relates to encapsulating microelectronic dies in the manufacturing of memory devices, microprocessors and other types of microelectronic devices.
Many packaged microelectronic devices have a substrate, a microelectronic die attached to the substrate, and a protective covering encasing the die. The protective covering is generally a plastic or ceramic compound that can be molded to form a casing over the die. The microelectronic die can be a memory device, a microprocessor, or another type of microelectronic assembly having integrated circuitry. Several types of packaged devices also include bond pads on the substrate that are coupled to the integrated circuitry of the die. The bond pads may alternatively be coupled to pins or other types of terminals that are exposed on the exterior of the microelectronic device for connecting the die to buses, circuits and/or other microelectronic assemblies.
A significant limiting factor for manufacturing packaged microelectronic devices is encapsulating the die with the protective covering. The dies are sensitive components that should be protected from physical contact and environmental conditions to avoid damaging the die. The protective casing encapsulating the die, therefore, should seal the die from the environmental factors (e.g., moisture) and shield the die from electrical and mechanical shocks.
One conventional technique for encapsulating the die is known as xe2x80x9ctransfer-molding,xe2x80x9d which involves placing the die and at least a portion of the substrate in a cavity of a mold and then injecting a thermosetting material into the cavity. The thermosetting material flows over the die on one side of the substrate until it fills the cavity, and then the thermosetting material is cured so that it hardens into a suitable protective casing for protecting the die. The protective casing should not have any voids over the die because contaminants from the molding process or environmental factors could damage the die. The thermosetting material, moreover, should not cover a ball-pad array on the substrate or damage any electrical connections between the die and the substrate. Therefore, it is important to control the flow of the thermosetting material in the cavity to avoid (a) producing voids in the protective casing over the die, (b) covering portions of the substrate with the thermosetting material that are not to be covered with the protective covering, and (c) displacing or otherwise damaging any wiring or solder joints between the die and the substrate.
One drawback of transfer-molding is that it is difficult to avoid producing voids in the thermosetting material. In one particular transfer-molding technique, a first protective casing is formed over the die on a first surface of the substrate, and a second protective casing is formed over contacts on the die and wire-bond connections on a second surface of the substrate. The first casing is formed from a first flow of the thermosetting compound, and the second casing is formed from a second flow of the thermosetting compound. This transfer-molding technique may result in voids along either the first or second surface of the substrate because the first and second flows may counter one another as they flow through the mold. Other transfer-molding techniques may also produce voids in the protective casing over the die because the flow of the thermosetting material in the mold may produce a first flow section that moves in a direction counter to a second flow section. Therefore, it would be desirable to eliminate voids in the protective casing.
The present invention is directed toward methods and apparatuses for encapsulating a microelectronic die or another type of microelectronic device. One aspect of the present invention is directed toward packaging a microelectronic die that is attached to either a first surface or a second surface of a substrate. The die can be encapsulated by positioning the die in a cavity of a mold and sealing the substrate to the mold. The method can further include injecting an encapsulation compound into the cavity at a first end of the substrate so that the compound moves along the first surface of the substrate. This portion of the compound defines a first flow of compound along the first surface that moves in a first direction from a first end of the mold toward a second end of the mold. The method can also include driving a portion of the compound through the substrate at a pass-through location or a secondary gate that is spaced apart from the first end of the substrate to generate a second flow of compound along the second surface of the substrate. The second flow of compound moves in a second direction toward the first end of the mold. As the first and second flows of compound move through the mold, the method includes inhibiting a third flow of compound from moving in the first direction along the second surface of the substrate between the first end of the substrate and the pass-through location.
Another aspect of this invention is a microelectronic device comprising a substrate, a microelectronic die attached to substrate, and a cover encasing at least a portion of the die. The substrate can have a first surface, a second surface, and plurality of ball-pads on the second surface. The microelectronic die can have a first side attached to the first surface of the substrate, a plurality of contacts on the first side, and an integrated circuit coupled to the contacts. The contacts of the die can be electrically coupled to the ball-pads of the substrate by a plurality of connectors. The cover can further include a first casing encapsulating the die and a portion of the first surface of the substrate, and a second casing encapsulating the contacts on the first side of the die and the connectors. The first casing has a first end, a second end, a first gate section at the first end, and a second gate section also at the first end. The first and second gate sections are spaced apart from one another along the first end.